The higher prevalence of myopia in Asian cities has also been linked to an indoor lifestyle, as a greater exposure to natural sunlight can increase the eye’s protection against conditions such as myopia.

“The protective effect seems to be associated with total time outdoors, rather than with specific engagement in sport,” said the study's authors.

Experts also believe that eye conditions are the key to spotting underlying health issues.

Ophthalmologists can detect and diagnose a range of medical conditions - from eye diseases such as cataracts and glaucoma, to systematic illnesses such as diabetes, cardiovascular disease and liver disease - just by looking at a person's retina.